Recently, a waterborne coating composition has been widely used in place of the solvent type coating composition when articles made of metal such as outer panels and parts of vehicles such as automobiles and two-wheel vehicles are coated. Although there is a demerit that the waterborne coating composition is generally inferior in water resistance in comparison with the solvent type coating composition, for example, a coating composition containing a waterborne curable resin composition containing a carbodiimide compound is proposed for improved water resistance of the waterborne coating composition (for example, JP-A-2001-11151).
JP-A-2003-306476 discloses a carbodiimide compound and a waterborne curable resin composition containing thereof with a purpose of further improved water resistance. According to JP-A-2003-306476, curing at comparatively low temperature can be carried out by adding a carbodiimide compound to a coating composition, and a coating composition superior in properties such as water resistance can be obtained.